1: 93.2 percent / pyridine / toluene / 24 h / Ambient temperature 2: 60 percent / AcOH, tetrabutylammonium fluoride / tetrahydrofuran / 6 h / Ambient temperature 3: 56 percent / POCl3, triethylamine / hexane; toluene / Ambient temperature 4: 25 percent / pyridine / 240 h / Ambient temperature View Scheme